1. Field of the Invention
The present invention relates to surveillance cameras, and, more particularly, to surveillance cameras that undergo tilt movements.
2. Description of the Related Art
Surveillance camera systems are commonly used by retail stores, banks, casinos and other organizations to monitor activities within a given area. The cameras are often provided with the capability to pan and tilt in order to acquire images over a wide domain. The tilt of the camera generally refers to the pivoting of the camera about a horizontal axis that is parallel to the floor, such that the lens of the camera may tilt between an upwardly pointing position and a downwardly pointing position. The pan of the camera refers to the rotation of the camera about a vertical axis that is perpendicular to the floor, such that the lens may scan from side to side. The cameras may also be able to zoom in order to reduce or enlarge the field of view.
A problem is that a pan-tilt-zoom camera can view only a small portion of a room at a time. Thus, an entire room cannot be continuously monitored by use of a pan-tilt-zoom camera, either by human personnel or by a surveillance algorithm. That is, in order to provide the capability to acquire a high-resolution image of distant objects, traditional high-zoom pan-tilt surveillance cameras view only a small part of the total possible viewing domain at any given time.
A large-domain sensor is capable of sensing an entire room at one time, but with lower resolution. So it is therefore desirable to combine it with a high-resolution pan-tilt-zoom camera. There are limitations when combining a large-domain sensor with a pan-tilt camera, however. Most installations position the camera in a downward-facing orientation so the user may track moving objects that pass underneath. Therefore, the stationary pan base is above the moving pan and tilt stages. If a sensor platform were to be provided on a moving camera in this orientation such that the sensor platform is disposed low enough to have an unobstructed view in all directions, then the sensor platform would also obstruct the view of the camera. If the sensor were to be positioned to one side of the stationary camera pan base, then multiple sensors would be needed in order to provide adequate coverage, and even then the area directly beneath the camera may be obstructed. Because of these problems, the system-level integration needed to provide continuously uninterrupted sensor coverage with multiple sensors introduces complications and adds cost. Another problem with this approach is that if the sensor is located on the moving pan stage but is not positioned precisely on the pan axis, then the system algorithms that use inputs from the sensor must compensate for the changing position of the sensor as the unit pans.
What is neither disclosed nor suggested by the prior art is a surveillance camera arrangement including both a large-domain sensor and a pan-tilt-zoom camera in a same hemispherical dome window, wherein the field of view of the pan-tilt-zoom camera is unimpeded by the large-domain sensor.